The surface charge density effect on the electro-osmotic flow in a nanochannel: a molecular dynamics study

The electro-osmotic flow of an aqueous solution of NaCl between two parallel silicon walls is studied through a molecular dynamics simulation. The objective here is to examine the dependency of the electro-osmotic flow on the surface charge density by considering the changes made in the structural properties of the electric double layer (EDL). The ion concentration, velocity profiles, and electric charge density of the electrolyte solution are investigated. Due to the partially charged atoms of the water molecules, water concentration is of a layered type near the wall. The obtained profiles revealed that an increase in the surface charge density, at low surface charges where the governing electrostatic coupling regime is Debye-Huckel, increases both the electro-osmotic velocity and the EDL thickness; whereas, a decreasing trend is observed in these two parameters in the intermediate regime. For high values of surface charge density, due to the charge inversion phenomenon, the reversed electro-osmotic flow will be generated in the channel. Results indicate that the absolute value of the reversed electro-osmotic velocity rises with an increase in the surface charge density.